This invention relates to methods and apparatus for gravel packing a single zone in a well.
When producing fluids from one or more zones in a well, it is sometimes desirable to gravel pack the zone or zones from which fluid is being produced. Such packing is helpful in cases where the well is in an unconsolidated formation. When fluid flows through such a formation into the well bore, loose formation sand and the like may be carried with the fluid into the bore and produced to the surface of the well. This situation is harmful both to the formation, causing its collapse and preventing further fluid flow, and to the producing equipment, causing severe wear.
In order to prevent such production in unconsolidated formations, a fine gravel pack is placed in the bore at the level of the zone from which fluid is to be produced. Typically, the well bore is cased and perforated at a production zone, although open holes (uncased well bores) are packed as well. A plug is used to seal the bore beneath the zone. Immediately above the plug, a slotted screen or liner is positioned adjacent the zone and a fine gravel is packed on all sides of the screen. Fluids are then produced from the zone through the gravel pack which acts as a filter to prevent production of particulate matter from the formation to the surface of the well.
Various downhole tools provide means for lowering a screen to a selected zone and packing gravel about the screen. Such tools are typically lowered on tubing and include conduits which connect the tubing to the lower part of the tool at which point the screen is suspended. A gravel slurry is pumped down the tubing to the exterior of the screen to deposit gravel about the screen. The fluid from the slurry passes through the screen and returns to the surface of the well in the bore annulus. Many past tools are designed for packing more than one zone in a single well and may require more than one trip to the level of the zone being packed. All of the tools, whether designed for single or multiple zone packing, include various means whereby ports or valves are open and closed, typically in response to tubing manipulation by the well operator, to either treat the zone with a fluid prior to packing or to change the fluid-flow configuration in the tool subsequent to packing in order to clean the tubing and annulus with a clean fluid. Such opening and closing is often effected by shearing pins. Tools with such ports or valves are disadvantageous due to their mechanical complexity.
In contrast, the present invention overcomes all of the limitations and disadvantages of the prior art by providing a new and advantageous method and apparatus for gravel packing a zone in a well in which packing and thereafter flushing the downhole equipment is achieved without manual operation of downhole ports or valves. A further advantage of the present invention includes provision of an apparatus which permits setting a screen on the bottom of a well without the necessity of establishing a reference and without damaging the screen.
The present invention includes coaxially aligned inner and outer conduits which depend downwardly from a crossover that is adapted to be suspended from the bottom of a tubing string. The crossover permits fluid communication between the tubing string and the annulus between the inner and outer conduits as well as between the inner conduit and the annulus between the tubing and the casing. Beneath the crossover, an elastomeric packer extends about the circumference of the outer conduit. Anchor slips are provided beneath the packer to permit compression of the packer into a bore-sealing condition when the slips are anchored in the bore. A slidable screen support is positioned over the outer conduit beneath the packer. A clutch interconnects the screen support with the conduit, such being engaged so as to transmit rotary and longitudinal movement to the screen support when the support is at its lowermost position on the conduit. A screen is threadably attached to the support.
When the apparatus is lowered into a well bore and when the screen hits the bottom, the clutch between the support and outer conduit disengages and permits tubing string manipulation to effect setting of the anchor slips and compression of the packer. Thereafter, a gravel slurry is pumped down the tubing to deposit gravel about the screen. The fluid passes through the screen and returns to the surface via the inner conduit and the bore annulus. After packing, the packer seal is disengaged and a clean fluid is circulated downwardly through the bore annulus and then upwardly in the tubing to flush out gravel which might be present. The tubing is raised to engage the clutch and then rotated to unscrew the screen and thereafter raised to the surface leaving the gravel packed screen downhole.
These and other attendant advantages of the instant invention will become apparent in view of the following detailed description and the accompanying drawings.